This invention relates to a V-ribbed belt, and particularly relates to techniques for reducing vibration and noise thereof.
V-ribbed belts of such kind are conventionally well known and generally put into wide use as belts for driving engine accessories or other purposes. For example, Japanese Patent Application Laid-Open Gazettes Nos. 9-236156 and 9-273607 propose a technique of using ethylene-2,6-naphtalate fibers (PEN fibers) as a material for a tension member (cord) embedded into a V-ribbed belt thereby increasing resistance to flexural fatigue of the belt or reducing the slip ratio thereof.
Meanwhile, in recent years, as the quietness of a vehicle engine has been increasingly enhanced, vibration and associated noise in a driving device for an engine auxiliary have been relatively intensified.
In order to reduce such vibration and noise, there have been conventionally employed a method of using a V-ribbed belt of increased tension or a technique of adjusting the layout of an engine auxiliary driving device including a V-ribbed belt to press an idler pulley against the back face of the belt in a span between pulleys.
However, a power transmission belt generally has the characteristic of reducing its tension due to creep of its tension member or wear of itself. Therefore, if the belt is adjusted to increase its tension in the above conventional manner, this invites inconveniences such as increase in the frequency of maintenance for tension management. It is substantially impossible to ask general users to carry out such maintenance.
On the other hand, if an idler pulley is arranged to press a belt portion located in the span between pulleys, a space for supporting the idlerpulley is necessary. This invites higher cost.
An object of the present invention is to suppress production of vibration and associated noise during the running of a V-ribbed belt without the need for tension management of the belt and provision of an idler pulley by appropriately setting characteristics such as the shape or material of the V-ribbed belt.
To attain the above object, in the present invention, a tension member of a V-ribbed belt has a high spring constant or a high damping constant or the flexural rigidity of the belt is enhanced, thereby reducing vibration of the belt caused in its span between pulleys. Alternatively, a rubber portion of the belt is thickened so that a shock caused when the belt strikes a pulley can be cushioned.
More specifically, an aspect of the present invention is directed to a V-ribbed belt in which a tension member is embedded and a plurality of ribs are formed in a bottom face thereof to extend in parallel with one another along the length of the belt, and the V-ribbed belt is characterized in that the dimension from a rib-side end of the tension member to a rib bottom is set in the range of 1.0 to 2.0 mm.
With this construction, since the bottom-side portion of the V-ribbed belt is sufficiently large in thickness, a shock caused when the belt vibrates and strikes a pulley can be cushioned and noise associated with the vibration (noise produced by the strike of the belt on the pulley) can be reduced. If the dimension from the rib-side end of the tension member to the rib bottom is below 1.0 mm, the effect of cushioning the shock cannot sufficiently be acquired. On the contrary, if the dimension is over 2.0 mm, the resistance of the belt to flexural fatigue is lowered and the belt life is shortened. Therefore, the dimension from the rib-side end of the tension member to the rib bottom is set in the range of 1.0 to 2.0 mm.
A second aspect of the present invention is directed to the same V-ribbed belt as that of the first aspect, and characterized in that the dimension from a rib-side end of the tension member to a rib top is set in the range of 3.0 to 4.0 mm. With this construction, since the flexural rigidity of the belt is enhanced, the belt becomes difficult to vibrate in its span between pulleys. As a result, vibration and associated noise of the belt can be reduced. If the dimension from the rib-side end of the tension member to the rib top is below 3.0 mm, the flexural rigidity cannot sufficiently be enhanced. On the contrary, if the dimension is over 4.0 mm, the resistance of the belt to flexural fatigue is lowered and the belt life is shortened. Therefore, the dimension from the rib-side end of the tension member to the rib top is set in the range of 3.0 to 4.0 mm.
A third aspect of the present invention is also directed to the same V-ribbed belt as that of the first aspect, and characterized in that the V-ribbed belt is set to exhibit a dynamic spring constant of 170 N/mm or more per rib when subjected to a dynamic response test which is conducted to grip a specimen of the belt in developed condition between fixed and movable chucks spaced 150 mm apart from each other and vibrate the specimen lengthwise of the belt by throwing repeated loads of 490.3xc2x1147.1 N at a vibration frequency of 50 Hz on the movable chuck, (i.e., a dynamic spring constant of 850 N/m or more for five ribs when the belt specimen is subjected to the same dynamic response test). With this construction, since the spring constant of the belt is sufficiently large, the belt is difficult to vibrate in its span between pulleys. As a result, vibration and associated noise of the belt can be reduced. If the dynamic spring constant of the belt is smaller than 170 N/mm, the effect of reducing vibration of the belt becomes insufficient. Therefore, the dynamic spring constant of the belt is set at 170 N/mm or more.
A fourth aspect of the present invention is also directed to the same V-ribbed belt as that of the first aspect, and characterized in that the V-ribbed belt is set to exhibit a dynamic damping constant of 0.013 Nxc2x7S/mm or more per rib when subjected to the same dynamic response test (i.e., a dynamic damping constant of 0.065 Nxc2x7S/mm or more for five ribs when the belt specimen is subjected to the same dynamic response test). With this construction, since the damping constant is sufficiently large, the belt is difficult to vibrate in its span between pulleys. As a result, vibration and associated noise of the belt can be reduced. If the dynamic damping constant is smaller than 0.013 Nxc2x7S/mm, the effect of reducing vibration of the belt is insufficient. Therefore, the dynamic damping constant of the belt is set at 0.013 Nxc2x7S/mm or more.
A fifth aspect of the present invention is also directed to the same V-ribbed belt as that of the first aspect, and characterized in that when the V-ribbed belt is subjected to a flexural rigidity test which is conducted to place the belt between a pair of upper and lower pressing plates of a testing device constructed such that the upper and lower pressing plates are held in parallel with each other by a pair of links to form a parallelogram by both the pairs of pressing plates and links and set a weight of 6.86 N on the upper pressing plate to deform the belt in a flat-like shape, the flexural rigidity of the V-ribbed belt determined, based on the distance 1 (unit: cm) between both portions of the tension member located respectively in upper and lower spans of the belt in deformed condition, from the following formula:
Flexural rigidity (unit: Nxc2x7cm2)=0.174xc3x97Wxc3x9712,
is 7.84 Nxc2x7cm2 or more per rib (i.e., the flexural rigidity of the V-ribbed belt subjected to the same flexural rigidity test is 39.2 Nxc2x7cm2 or more for five ribs). With this construction, since the flexural rigidity of the belt is enhanced, the belt becomes difficult to vibrate in its span between pulleys. As a result, vibration and noise of the belt can be reduced. If the flexural rigidity of the belt is less than 7.84 Nxc2x7cm2, it cannot sufficiently be enhanced. Therefore, the flexural rigidity of the belt is set at 7.84 Nxc2x7cm2 or more.